Arctic Sea Ice

1. The Cryosphere

As ESA Earthnet describes, almost 80% of the Earth's fresh water is locked up in the cryosphere, i.e. snow, ice and permafrost. The cryosphere plays an important role in moderating the global climate – and as such, the consequences of receding ice cover due to global warming are far reaching.

Albedo change: Snow cover on the ice reflects between 80% and 90% of sunlight, while the dark ocean without ice cover reflects only 7% of the light, explains Stephen Hudson of the Norwegian Polar Institute. As the sea ice cover decreases, less solar radiation is reflected away from the surface of the Earth in a feedback effect that causes more heat to be absorbed and consequently melting to occur faster still.

2. Sea Ice Extent

The image below (by Kinnard et al. 2011) shows a reconstructed history of late-summer Arctic sea ice extent over the period AD 561–1995.

Ice extent has continued to decrease dramatically since 1995. Below are the figures for recent years as calculated by the U.S. National Snow and Ice Data Center (NSIDC).

Year of September Average Extent

Extent (million sq. km)

2002

5.96

2003

6.15

2004

6.04

2005

5.57

2006

5.89

2007

4.28

2008

4.67

2009

5.36

2010

4.90

2011

4.61

September Average Extents, 2002-2011, National Snow and Ice Data Center NSIDC

Note that above figures are for the average September extent, and thus somewhat higher than the annual minimum.

The 2007 Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) in many respects underestimated the severity of global warming and the speed at which it strikes, as described in more detail in the post Global Warming - Red Alert!

An April 2007 news release accompanying a study by Stroeve et al. said "the shrinking of summertime ice is about 30 years ahead of the climate model projections. As a result, the Arctic could be seasonally free of sea ice earlier than the IPCC- projected timeframe of any time from 2050 to well beyond 2100." The news release featured the image below, showing observations of sea ice extent far worse than the worst IPCC projections.

Below, the image is updated with later observations (September 2007 and 2008).

NSIDC recently featured an updated version (image below) showing the observed September sea ice extent for 1952 to 2011 (black line) against a backdrop of two models (in red and blue). The recently observed decline is even steeper than projected by RCP 4.5, a scenario that would make the global temperature rise soon exceed 2 degrees Celsius.

The NSIDC image below shows that sea ice extent reached at August 5, 2012, reached a record low for the time of year.

For updates, see the daily images produced by the NSIDC. Note that, to calculate extent, the NSIDC includes areas that show at least 15% sea ice. In the image below, from the Danish Meteorological Institute, areas with ice concentration higher than 30% are included to calculate ice extent.

The Danish Meteorological Institute also produces graphs showing that include areas with ice concentration higher than 15% to calculate ice extent. In this case, extent will obviously appear to be larger (see scale on left-hand side) than in above graph.

The grey shaded area corresponds to the climate mean plus/minus 1 standard deviation.

3. Sea Ice Area

Sea ice area differs from sea ice extent, as described in te NSIDC FAQ page:

A simplified way to think of extent versus area is to imagine a slice of Swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. That is why if you compare extent and area in the same time period, extent is always bigger.

Old versus new ice in Arctic: The maps show the median age of sea ice in March 1985 (left) and March 2011 (right).
Overall, the proportion of old ice has decreased. By March 2011, ice over 4 years old accounts for less than
10% of the Arctic ice cover. Credit: National Snow and Ice Data Center, University of Colorado, Boulder.

In a comment at skepticalscience.com, Dikran Marsupial posted the two graphs below, based on PIOMAS data and with a prediction added in red, adding that the usual caveats about this being a purely statistical projection apply. Indeed, there are a number of ways in which extrapolation of data can be done.

Given the many feedbacks that reinforce each other and only now are starting to kick in, observed data do not fit a linear trend very well, as also illustrated by the three graphs below for minimum volume, again based on PIOMAS data, with trend lines added by Wipneus.

The exponential trend on above image pointing at 2015 appears to fit observed data much better than the straight line on the image below.

The image below, by Wipneus and earlier published at the Arctic Sea Ice Blog, illustrates that sea ice volume is on track to reach a minimum of 3000 cubic kilometers later in 2012.

As the image on the left shows, current trends point at the imminent loss of all Arctic sea ice within a few years.

Some expect that some ice will persist close to Greenland for at least a few years more, since Greenland constitutes a barrier that holds the sea ice in place.

Nonetheless, a virtually complete collapse of the sea ice could be brought about by more intense storms and heavy winds, which can be expected as more of the Arctic Ocean turns into open sea and as waters warm up in summer.

The thinner the sea ice gets, the more likely an early collapse is to occur. There is robust evidence that global warming will increase the intensity of extreme weather events, so more heavy winds and more intense storms can be expected to increasingly break up the remaining ice in future, driving the smaller parts out of the Arctic Ocean more easily. Much of the sea ice loss already occurs due to sea ice moving along the edges of Greenland into the Atlantic Ocean.

For more background, also see the related post at the Arctic-news blog and the comments underneath.

5. Albedo

The ocean reflects only 6% of the incoming solar radiation and absorbs the rest, while sea ice reflects 50% to 70% of the incoming energy. Thick sea ice covered with snow reflects as much as 90% of the incoming solar radiation. After the snow begins to melt, and because shallow melt ponds have an albedo of approximately 0.2 to 0.4, the surface albedo drops to about 0.75. As melt ponds grow and deepen, the surface albedo can drop to 0.15. [ source: NSIDC.org ]

6. Radiative Forcing

Snow and ice on the Northern Hemisphere has an average cooling effect of 2.2 to 4.6 Watts per square meter, peaking in May at ~ 9 Watts per square meter, as shown on above image from Flanner et al.

Snow and ice on the Northern Hemisphere is now reflecting 0.45 watts less energy per square meter than it did in 1979, as shown on above image from Flanner et al. This compares to warming of 1.66 watts per square meter for carbon dioxide (at 379 ppm, 2005 levels, IPCC) and 0.48 per square meter for methane (1774 ppb, 2005 levels, IPCC).

7. Some implications of Ice Loss

As said, the cryosphere plays an important role in the global climate, which affects global food supply. The more snow and ice melts, the more heat gets absorbed in the Arctic, as illustrated in above image that also shows a huge change in warming on the Himalaya Tibetan plateau, where glaciers are melting at record speed, while the blue areas indicate desertification in China and Mongolia.

Above image shows how much organic carbon is present in the melting permafrost, illustrating the potential for wildfires as temperatures keep rising in the Arctic. Releases of methane in the Arctic could accelerate this rise significantly. Much of the soot from firestorms in Siberia could settle on the ice in the Himalaya Tibetan plateau, further contributing to the melting of glaciers there and causing short-term flooding followed by rapid decrease of the flow of ten of Asia’s largest river systems that originate there, while more than a billion people’s livelihoods depend on the continued flow of this water.

Videos

Global temperatures are rising fast. In the Arctic, temperatures are rising even faster (interactive charts below and right). For 2010 and 2011, NASA recorded anomalies of over 2°C at higher latitudes (64N to 90N), with anomalies of over 3°C at latitudes 79N and 81N in 2010.

For November 2010, anomalies of 12.5°C were recorded at latitude 71N, longitude -79 (Baffin Island, Canada). At specific moments in time and at specific locations, anomalies can be even more striking. As an example, on January 6, 2011, temperature in Coral Harbour, located at the northwest corner of Hudson Bay in the province of Nunavut, Canada, was 30°C (54°F) above average.